1. Field of the Invention
The present invention pertains to methods and systems for coupling fiber optic cables and more particularly to coupling systems that automatically compensate for changes in light intensity at the output end of fiber caused by changes of light intensity from the source, beam walking at input of fiber, and mode changes in fiber.
2. Related Prior Art
Prior art has disclosed many methods of transmitting a light beam and producing an output. The output may be used to illuminate a sample or may use the transmitted light for any one of many purposes. The following United States patents are representative of the many different types of coupling systems that have been developed to intercede between a light source and an fiber optic cable to improve light transmission or even to produce a modified light output with a different use. Also included are patents which relate to another aspect of the system in which the present invention may be used, frequency multipliers.
U.S. Pat. No. 4,240,048, titled "Nonlinear Optical Device", issued to Fredrick C. Zumsteg, relates to a nonlinear optical device having a crystal which has nonlinear optical properties and is transparent to the radiation propagating through it. It also has predetermined symmetry and consists essentially of the compound of the formula: EQU LnF.sub.x (OH).sub.1-x CO.sub.3
wherein Ln is La, Eu or Gd and x is 0 to 1. The preferred compound is LaOHCO.sub.3.
U.S. Pat. No. 4,272,694, titled "System for Converting the Frequency of Coherent Radiation", issued to Stephen D. Jacobs, relates to a system where coherent radiation which may be provided at high power and in a wide aperture beam is tripled in frequency by Type II crystals having non-linear optical coefficients. A waveplate along the beam path between the crystals corrects ellipticity which limits the conversion efficiency of the system.
U.S. Pat. No. 4,504,949, titled "Stimulated Anti-stokes Raman Up-Converter", issued to Jonathan C. White, relates to an anti-Stokes Raman up-converter which is capable of up-converting a variety of conventional laser sources. A metal-halide such as thallium chloride or thallium iodide is employed as a lasing medium, and is photo-dissociated to create a population inversion in a metastable state of the metal ion. An excimer laser may be employed to photo-dissociate the metal halide. In the alternative, an excimer flashlamp may be employed to photo-dissociate the metal-halide. A conventional laser source is subsequently employed to pump the population inversion from the metastable state to a virtual level near an intermediate state. Anti-Stokes Raman lasing occurs from this virtual state, where the lasing frequency is greater than the frequency of the conventional laser pump source.
U.S. Pat. No. 4,618,957, titled "Frequency Doubling A Laser Beam by Using Intracavity Type II Phase Matching", issued to Kuo-Ching Liu, relates to a frequency doubler for a laser in which a Type II SHG crystal is oriented to generate a second harmonic frequency beam in response to the orthogonal components of a fundamental beam. After the fundamental beam makes a round trip through the SHG crystal, and differential phase delays between the E and O rays of the fundamental beam due to birefringence are eliminated. This is done to improve the efficiency and stability of the cavity.
U.S. Pat. No. 4,700,150, titled "External Laser Frequency Stabilizer", issued to John L. Hall and Theodor W. Hansch, relates to an external laser frequency stabilizer which combines an acousto-optic frequency shifter and a fast electro-optic phase modulator. A compensating electronic delay line in a crossover network is used to provide a transducer response while keeping the voltage across the electro-optic crystal away from the amplifier limits.
U.S. Pat. No. 4,538,278, titled "Apparatus and Method for Generating LIght in the Near Ultraviolet to Infrared Range", issued to John S. Gergely, relates to a source of linearly polarized light having a wavelength range of about 550 to 1100 nanometers to provide light into one end of an optical fiber. A nonlinear crystal of the type that mixes the frequency of light passing therethrough is positioned adjacent the other end of the fiber. The fiber transmits light from the source to the crystal which increases its frequency up to 100%, dependent upon crystal selection providing light in the 250-550 nanometer wavelength range. Adjusting the radial orientation of the crystal with respect to the fiber optimizes conversion of light to the 250-550 nanometer range. Such light is directed into organic dye which emits fluorescent light in the range of about 400 to 1000 nanometers dependent upon the type of dye selected.